Animal DigestionAnimal Digestion

Name, locate and describe the Name, locate and describe the functions of the parts of the functions of the parts of the

digestive system.digestive system.

IntroductionIntroduction Digestion is defined as the breakdown Digestion is defined as the breakdown

of nutrientsof nutrients We consume: We consume:

ProteinsProteins

CarbohydratesCarbohydrates

FatsFats

Nucleic acidsNucleic acids These are broken down into their These are broken down into their

simplest formssimplest forms

And that’s not all…And that’s not all…We also consume:

Water – is not digested1. Hydrates body’s cells2. Enables transport and exchange of materials

to and from the cells Gases Nutrients Waste

3. Regulates body temperature Vitamins / Minerals (living source) / (non-living source)

*These are needed in trace amounts to assist reactions in the cells

From Beginning to EndFrom Beginning to End

MouthEsophagusStomach

Small intestineLarge intestine

Anus

MouthMouth Point at which Point at which ingestioningestion takes place takes place

and where food is chewed. and where food is chewed. Site that begins Site that begins mechanicalmechanical and and

chemicalchemical digestion of food digestion of food Mechanical digestion = chewingMechanical digestion = chewing Chemical digestion = secretion of salivaChemical digestion = secretion of saliva

Teeth Teeth provideprovide mechanical mechanical

digestion digestion of food by of food by breaking, cutting, breaking, cutting, and tearing.and tearing. The The increased

surface area : : aids in the aids in the

swallowing swallowing process. process.

Allows more Allows more efficient digestion efficient digestion by chemicals.by chemicals.

Salivary GlandsSecrete saliva which: Secrete saliva which: moistensmoistens the food (makes it slippery) the food (makes it slippery) stimulatesstimulates taste taste BeginsBegins chemical digestion chemical digestion

Saliva contains the Saliva contains the enzymes:enzymes: salivary amylase salivary amylase salivary maltase salivary maltase

**EnzymesEnzymes are are organic catalystsorganic catalysts that that speed up chemical reactionsspeed up chemical reactions without being altered without being altered by the by the reaction. reaction.

Saliva includes:Saliva includes: Water: moistens consumed feed and

aids in the taste mechanisms.

Mucin: lubrication aid for swallowing.

Bicarbonate Salts: acts as a buffer to regulate pH of the stomach.

Enzymes: salivary amylase/maltase initiates carbohydrate breakdown.

Esophagus: hollow, muscular tube that transports “bolus” from the mouth to the stomach; Ingested material is moved by a

series of muscular contractions referred to as peristaltic waves.

Cardiac Sphincter: valve at the junction of the stomach and esophagus.

Stomach: hollow, pear shaped, muscular digestive organ

Structures Beyond the Mouth…Structures Beyond the Mouth…

Functions of StomachFunctions of Stomach (Site of Digestion) (Site of Digestion)

Muscular movements cause physical breakdown by grinding food between folds (called

rugae).

Secretes digestive juices for chemical breakdown:

1) Hydrochloric Acid2) Pepsin3) Rennin

Parts of the stomach:Parts of the stomach: Cardiac sphincter-

prevents backflow

Esophageal region: non-glandular area surrounding the cardiac sphincter

Cardiac gland region: contains cells that produce primarily mucus (protects stomach lining)

Fundic gland region: contains cells that provide the gastric secretions needed for the initial stages of digestion.

Parietal cells: produce hydrochloric acid. Chief cells: produce enzymes or precursors of

enzymes

Pyloric gland region: contains cells that produce mucus and some proteolytic (protein digesting) enzymes.

Pylorus sphincter: at the beginning of the small intestine which controls passage of material (chyme) out of the stomach

Stomach contents approximately a pH of 2 (kills bacteria).

Material arriving at the stomach is called the bolus

Material leaving the stomach is called chyme.

Just a Reminder……

Both types of digestion are occurring in the stomach:

Mechanical and Chemical

The churning of the stomach is considered mechanical digestion

The enzyme activity is considered chemical digestion

Chemical > Mechanical

Small Intestine - Small Intestine - 3 sections3 sections

1. Duodenum (first section) Receives secretions from:

Pancreas: acts on proteins, carbohydrates and lipids

Liver: bile (stored in the gallbladder) breaks down fat.

Active site of digestion

2. Jejunum: (middle section) active in nutrient absorption

3. Ileum: (last section) active in nutrient absorption

PancreasPancreas

EndocrineEndocrine InsulinInsulin glucagonglucagon

ExocrineExocrine Enzymes Enzymes

(acini)(acini) BicarbonatBicarbonat

e (ducts)e (ducts)

Small IntestineSmall IntestineWalls of the S.I. are lined with a series of fingerlike projections

called villi, which in turn have minute projections

called microvilli that increase the

nutrient absorption area.

Small intestine cont’d…Small intestine cont’d… Each nutrient has a specific absorption

site.

Each villus contains an arteriole and venule, together with a drainage tube of the lymphatic system, a lacteal.

The venules ultimately drain into the portal blood system, which goes directly to the liver.

The lymph system empties via the thoracic duct into the vena cava.

S.I. contents are approximately pH 6 to 7. S.I. contents are approximately pH 6 to 7.

Sight of digestion and absorption.Sight of digestion and absorption. Passive absorptionPassive absorption = results from = results from diffusiondiffusion or or

movement from high concentrations to low movement from high concentrations to low concentrations.concentrations.

Active absorptionActive absorption = = transporttransport of molecules of molecules across the intestinal lining.across the intestinal lining.

(villi) engulf the molecules and then actively (villi) engulf the molecules and then actively transport these molecules to either the transport these molecules to either the bloodstream or the lymph. bloodstream or the lymph.

Nutrients are carried to the liver where it is Nutrients are carried to the liver where it is detoxified.detoxified.

Large Intestine – 3 sectionsLarge Intestine – 3 sections

1. CecumCecum (first sections)(first sections) size varies considerably in different species; size varies considerably in different species; Non-functional in humans (appendix)Non-functional in humans (appendix) Horses contain an active flora of bacteria Horses contain an active flora of bacteria

similar to the microbial population in rumen similar to the microbial population in rumen compartment of ruminants. compartment of ruminants. Bacterial breakdown of cellulose and other Bacterial breakdown of cellulose and other

carbohydrate material so the horse can carbohydrate material so the horse can utilize fibrous feeds. utilize fibrous feeds.

Site of Site of bacterial synthesis of of water-water-soluble vitamins and protein.soluble vitamins and protein.

2.2. ColonColon (middle section):(middle section): largest part of the large intestine largest part of the large intestine Primary area of Primary area of water restorationwater restoration from from

intestinal contents.intestinal contents.

3.3. RectumRectum (last section)(last section) the end of the digestive tract before the the end of the digestive tract before the

unabsorbed material (feces) is excreted unabsorbed material (feces) is excreted out the anus.out the anus.

4. AnusAnus: : • external opening where unabsorbed external opening where unabsorbed

materials (feces) are expelled from the materials (feces) are expelled from the body.body.

Functions of the L.I.Functions of the L.I. Site of water restorationSite of water restoration Secretion of some mineral elementsSecretion of some mineral elements

calciumcalcium Storage reservoir of undigested GI contents.Storage reservoir of undigested GI contents. Bacterial fermentation:Bacterial fermentation:

Synthesis of some Synthesis of some water-soluble water-soluble vitamins and vitamin K.vitamins and vitamin K.

Some bacterial breakdown of fibrous Some bacterial breakdown of fibrous ingredients.ingredients.

Synthesis of some Synthesis of some proteinprotein Limited absorption of feedstuff from the L.I.Limited absorption of feedstuff from the L.I.

Cross-section of Digestive Cross-section of Digestive TractTract

Defecation Reflex: Defecation Reflex:

mass movement mass movement

rectal distensionrectal distension

internal sphincter (invol) internal sphincter (invol)

external sphincter (vol)external sphincter (vol)

Bulk flow of liquid in gutBulk flow of liquid in gut Input

Ingestion ~ 2 litres per day Secretion (gut) ~ 7 litres/day

Output Faeces ~100 ml/day

Conclude ~ 9 litres/day absorbed Small intestine reabsorbs 7.5 L/day of water Large Intestine reabsorbs 1.4 L/day

Digestive Health: Protection & Problems

Immune defenseImmune defense: M-cells, Peyer's : M-cells, Peyer's patches, lymphocytespatches, lymphocytes

Irritable bowel diseaseIrritable bowel disease – chronic – chronic inflammationinflammation

DiarrheaDiarrhea: leads to dehydration (4 : leads to dehydration (4 million deaths/yr)million deaths/yr)

VomitingVomiting (emesis) can lead to alkalosis (emesis) can lead to alkalosis

UlcersUlcers- H. pylori- H. pylori

"heart-burn""heart-burn" acid reflux disease acid reflux disease

SummarySummary Processes of digestion: ingestion, digestion, absorption, secretion, motility, reabsorption & defecation

Anatomy of digestion: mouth, esophagus, stomach, small & large intestines, rectum, anus (pancreas & liver)

Enzyme hydrolysis of carbohydrates, proteins, lipids and nucleic acids provide the nutrients, absorbed & conducted to liver for storage and conversion

Some good websitesSome good websites http://kidshealth.org/kid/body/digest_noS

W.html http://www.teachnet.ie/farmnet/Digestive.

htm http://biology.clc.uc.edu/courses/bio105/d

igestiv.htm http://www.williamsclass.com/SeventhSci

enceWork/HumanBodySystemProject.htm